1. Field of the Invention
The present invention relates to a prober used for testing devices and to a testing apparatus using the prober.
2. Description of the Related Art
In typical manufacturing lines, in order to evaluate the electrical performance of devices under test (hereinafter referred to as “DUTs”), such as semiconductor devices and display panels, an apparatus called a prober for transporting and moving the DUTs to a measurement position is used together with a tester. Such a prober has a mechanism capable of moving along four axes, namely, three axes in x, y, and z directions and a rotational θ axis, to appropriately perform the transportation of the DUTs and their movement to the measurement position.
Conventionally, many commercially available probers have been designed to have positional accuracy on the order of microns or micro meters. However, with the miniaturization of semiconductors in recent years, the demand has arisen for probers having positional accuracy on the order of sub-micron. Thus, components using feedback control, which are referred to as “servo motors” or “servo amplifiers”, are now used.
In general, two types of servo motors, namely, AC (alternating current) and DC (direct current) motors, are available. AC servo motors that operate at a high speed, that do not produce dust due to a commutator and brushes, and that do not require less maintenance are mainly used for use semiconductor factories. After a low-AC-voltage power supply is converted into DC, silicon-controlled rectifiers, MOSFETs (metal-oxide semiconductor field-effect transistors), or IGBTs (insulated gate bipolar transistors) are used to switch three-phase high-frequency PWM (pulse-width modulated) inverters at several hundred Hz to several tens of kHz, and resulting outputs from the inverters are used to drive those servo motors.
That is, power converted from three-phase AC power supply into DC and converted back into AC is used for driving the AC servo motors. Since the re-conversion from DC into AC is performed using the inverters, relatively large noise may be generated. Such noise may affect the accuracy of measurements (voltage/current/resistance/charge) of a DUT placed on the chuck stage of the prober.
In a prober whose probe pins are brought into contact with a DUT in order to evaluate its performance, a relatively large current is used to produce high voltages in the prober so as to drive the motors. Thus, the influence of noise generated from the switching devices is considerable, and the performance of a measuring apparatus cannot be fully utilized.
For the measurement of semiconductor devices, with the miniaturization of semiconductors in recent years, a need has arisen for a measuring apparatus using currents on the order of femto-amperes and voltages on the order of micro-volts. In addition, for the measurement of flat-panel displays (FPDs), micro-charge measurement for measuring electrical charges held in storage capacitors that typically have a capacitance of 1 pF or less are required as well as high-speed measurements for an enormous number of pixels, typically exceeding 100,000.
Since display panels, such as conventional LCD (liquid crystal display) panels or organic EL (electroluminescent) panels, are fabricated by growing silicon on insulator glass, display-panel probers used for testing the display panels are designed to be suitable for SOI (silicon-on-insulation) structures in principle. Thus, there is no need to apply a potential to the insulator glass and, in essence, the ground potential is considered sufficient for the chuck potential. As a result, no particular consideration is given to the influence of noise on the measurement and thus no special provision is made for the chuck and its shield structure, as shown in FIG. 8 in Japanese Unexamined Patent Application Publication No. 2001-296547.
Recently, however, large glass substrates are mainly used in order to reduce the cost for display panels, thus necessitating consideration of the influence of the substrate size. For example, since fifth-generation large one-meter-square substrates are used in an amorphous silicon process, the operating range of the chuck stage requires a square area with 3 meters on each side. When such a large area is completely enclosed for shielding, the manufacturing cost is increased.
Known probers use their frame as a reference surface for the potential of the power supply, the servo amplifiers, and the servo motors and also as ground and a return path for a return current. In typical probers, because of the cost, shielded cables are not used for the power lines from the servo amplifiers to the motors. Also, no prober is available that uses shield cables whose braided portions are 360-degree shielded to eliminate the leakage of electromagnetic fields (e.g., cables surrounded by a grounded metal film along the longitudinal direction) for the cable extraction portions of the servo-motor housings. In this manner, since it is difficult to ensure shielding for known probers, high-frequency AC and DC signals, which are the main noise components, may be fed back to the servo amplifiers through the frame of the prober.
In addition, the increased size of the substrates also necessitates the consideration of the influence of the increased size of the chuck. When an insulator is interposed between the chuck and the ground, a stray capacitance (earth capacitance) C relative to the area S of the chuck is expressed by:C=∈r·(S/d)where ∈r indicates the dielectric constant of material of the insulator and d indicates the distance between the chuck and the ground.
Seventh-generation glass substrates have a size of about two meters on each side, that is, twice the size of the fifth generation substrates in terms of side length and four times as large as the fifth generation in terms of stray capacitance. As a result, paths through which noise is introduced into the chuck are easily formed. This means that the measuring apparatus for testing becomes more susceptible to influence from other path components.
In addition, since the display panel to be tested weighs more than a semiconductor wafer, a chuck-stage driving motor that uses a larger driving current is employed for the display-panel prober than for a semiconductor-device prober. Consequently, the display-panel prober generates a larger amount of noise than the semiconductor-device prober.
Accordingly, in order to achieve high-speed measurements of micro currents and micro charges, there is a need for a prober that suffers smaller influence on measurements from noise on the measurement.